The present invention relates to a keyboard for office machines, comprising: a series of keys each movable from a rest position to a working position, a group of code-bars movable along a predetermined trajectory, a group of springs for pulling said code-bars along said trajectory, a bridge for controlling said code-bars against the action of said group of springs and a series of setting elements selectable by each of said keys, when in said working position, for arresting some of said code bars against the action of the corresponding spring according to a corresponding code combination.
In one known keyboard of this type, by depressing a key a corresponding setting element is released and is placed by a corresponding spring in the paths of the code bars. A universal bar actuated, by the released element, in turn frees the bridge controlling the cams. The universal bar moreover, through a solenoid, recovers the released setting element and brings it back into the intital position against the action of the corresponding spring. The setting rate is rather limited, since owing to the single movement of the setting element through its spring, it is not possible to press a second key and to position a second setting element until the universal bar has returned the first setting element to its rest position.
A keyboard is also known in which a setting lug is pulled by a setting spring and is held by a releasable tooth of a selected setting element. The lug, when it is freed, shifts the selected setting element in order to position a plurality of code-bars by the same setting spring according to combinations of codes corresponding to the depressed key. The freed lug moreover operates a starting clutch, which restores the setting spring at the end of the setting cycle. This keyboard is very rapid in use, but, since the setting spring is given the duty of positioning the bars, it has to be fairly robust, and therefore the releasing means must be rather complex and expensive.